1. Field of the Invention
This invention relates to reduction and standardization of electric power consumption during daytime, and more particularly to a heat storage type air conditioning system with a heat storage tank containing a heat storage medium.
2. Description of the Prior Art
FIG. 16 is an explanatory diagram showing the arrangement of a conventional heat storage type air conditioning system disclosed, for instance, by Unexamined Japanese Patent Publication (Kokai) Hei-2-33573/(1990). The system comprises: a main refrigerant circuit 105 including a compressor 101, a condenser 102, a first pressure reducing mechanism 103, and an evaporator 104 which are connected in the stated order; a heat storing tank 107 containing a heat storing medium 106; a cold (low temperature) storing heat exchanger 108 for performing heat exchange between the heat storing medium 106 in the heat storing tank 107 and the refrigerant; a first bypass circuit 111 for allowing refrigerant to flow between a gas line 110 and a liquid line 109 extended between the condenser 102 and the pressure reducing mechanism 103 through the aforementioned heat exchanger 108; a second pressure reducing mechanism 113 connected to a liquid pipe 112 of the first bypass circuit 111; a refrigerant gas pump 114 for allowing heat exchange between the heat storage medium in the heat storage tank 107 and the refrigerant; a second bypass circuit 116 including the refrigerant gas pump 114 in such a manner that input and output terminals of the latter 114 are connected to a gas pipe 115 of the first bypass circuit 111; and a valve unit 117 for controlling the flow of refrigerant to the second bypass circuit 116.
Now, the operation of the conventional heat storage type air conditioning system thus organized will be described. The above-described circuit elements 101 through 104 are so connected that refrigerant flows to them through the refrigerant pipe line. In the main refrigerant circuit 105, the condenser 102 obtains cold (low temperature) through heat exchange with the air outside the room (hereinafter referred to as "outside air", when applicable), and the cold thus provided is applied to the air inside the room (hereinafter referred to as "inside air", when applicable) through the evaporator 104.
On the other hand, the system includes the heat storing o tank 107 containing the heat storing medium 106 which is able to store heat. The heat storing tank 107 incorporates the heat storing heat exchanger 108 adapted to perform heat exchange between the refrigerant and the heat storing medium 106 in the heat storing tank 107.
In an ordinary cooling operation, the second pressure reducing mechanism 113 is held closed, so that the refrigerant circulates in the main refrigerant circuit 105 only. That is, the refrigerant gas discharged from the compressor 101 is condensed by the condenser 102, and subjected to adiabatic expansion by the first pressure reducing mechanism 103, so that it is formed into a two-phase, gas and liquid, fluid at low temperature. The two-phase fluid flows into the evaporator 104, where it receive heat from outside; that is, it cools the surrounding air. The two-phase fluid itself evaporates, thus returning to the compressor 101. Hereinafter, the above-described operation will referred to as "a general cooling operation" when applicable, and a refrigerant flow circuit in the general cooling operation will be referred to as "a general cooling circuit" when applicable.
In a cold storing operation in which cold is stored in the heat storing tank 107 during nighttime in which electric power load is low, the first pressure reducing mechanism 103 is held closed. That is, the refrigerant gas discharged from the compressor 101 is condensed by the condenser 102, so that it is converted into a refrigerant at high temperature and at high pressure. The refrigerant flows into the first bypass circuit 111, and it is subjected to adiabatic expansion by the second pressure reducing mechanism 113, and then allowed to evaporate at the heat exchanger 108, thus cooling the heat storing medium 106 in the heat storing tank 107, so that cold is stored therein. Thereafter, the refrigerant itself evaporates, thus returning through the valve unit 117 to the compressor 101. Hereinafter, the above-described operation will be referred to as "a cold storing operation", when applicable, and a refrigerant flow circuit in the cold storing operation will be referred to as "a cold storing circuit", when applicable.
The system may perform a stored heat recovering operation in which cold stored in the heat storing tank 107 during nighttime is utilized. That is, when the refrigerant gas pump 114 is operated with the compressor 101 held stopped, a gas refrigerant at low temperature and at low pressure is increased in pressure by the refrigerant gas pump 114, and allowed to flow into the heat exchanger 108, thus giving heat to the heat storing medium 106. The refrigerant itself is condensed into a liquid. The liquid is subjected to adiabatic expansion by the second pressure reducing mechanism 113, so that it is converted into a two-phase, gas and liquid, fluid. The two-phase fluid flows into the evaporator 104, where it receives heat from outside, thus cooling the surrounding air. The fluid itself is allowed to evaporate; that is, it is gasified, thus returning to the refrigerant gas pump 114. Hereinafter, the above-described operation will be referred to as "a cold radiating operation", when applicable, and a circuit in which refrigerant flows in the cold radiation operation will be referred to as "a cold radiating circuit", when applicable.
The above-described air conditioning system is able to perform the general cooling operation, and the cold radiating operation in a parallel mode. That is, the system may be operated with both the compressor 101 and the refrigerant gas pump 114 in operation. More specifically, while the refrigerant condensed in the main refrigerant circuit 105 is allowed to evaporate by the evaporator 104, the refrigerant condensed by the heat exchanger 108 in the first bypass circuit 111 meets the refrigerant of the main refrigerant circuit 105, so that both the refrigerants are allowed to evaporate by the evaporator 104.
In the cooling operation, the ratio of the flow rate of the condensed refrigerant in the main refrigerant circuit to that of the condensed refrigerant in the bypass circuit is adjusted by controlling the operating capacity of the compressor 101 and the speed of rotation of the refrigerant gas pump 114, thus dealing with the air cooling load to the room.
Hence, when the general cooling operation and the cold radiating operation are performed in a parallel mode so that the stored cold is used for the cooling operation as much as required, electric power required for operation of the compressor 101 is standardized, reducing its maximum value.
The cold storing operation is carried out during the cold storing time period (ten to fourteen hours) in the night of the day the cooling operation has been carried out, and it may be performed with the residual ice left as it is, or it may be performed after the residual ice is molten.
The operation of the compressor 101 and the refrigerant gas pump in a parallel mode; that is, to perform the general cooling operation and the cold radiation operation in a parallel mode contributes effectively to a reduction of the load on the request for power consumption during daytime. However, the above-described method in which the refrigerants condensed by the condenser 102 and the heat exchanger 108 are allowed to meet each other, and are then allowed to evaporate by one and the same evaporator 104, suffers from the following difficulties: Depending on variations in environmental conditions such as inside air temperature and outside air temperature, and variations in the load on the side of the heat exchanger due to variation in temperature of the heat storing medium, the general cooling operation and the cold radiation operation become unbalanced in the quantity of refrigerant or in the quantity of ice machine oil. As a result, the operating conditions are adversely affected, so that the system is lowered in capacity. In addition, in each circuit, pressure rise or liquid back may take places when the quantity of refrigerant is abnormally increased or decreased, or the bearing of the compressor may be seized as a result of the shortage of ice machine oil; that is, there are unwanted conditions which may directly damage the refrigerant circuit parts.
In order to eliminate the above-described difficulties, the following method may be taken into consideration: In the method, the amounts of operation of the compressor and the refrigerant gas pump are controlled, so that the condensed refrigerant in the general cooling operation and the condensed refrigerant in the cold radiation operation are adjusted in flow rate. However, the method is not so effective as expected, because of the following reasons: The control method is rather intricate, and therefore the control equipment is high in cost, and it is required to increase the number of transmission lines of the control circuit. Furthermore, it is essential to add a mechanism (such as an invertor) for adjusting the capacity of the compressor or the refrigerant gas pump. That is, employment of the method results in an increase in running cost.
The cold storing operation, the general cooling operation, and the cold radiating operation are different in the required quantity of refrigerant from one another; that is, both the general cooling operation and the cold storing operation are less in the necessary quantity of refrigerant, whereas the quantity of refrigerant required for the cold radiating operation is relatively large. Hence, during the cold storing operation, a larger part of the quantity of refrigerant sealed in the whole circuit is surplus. When the cold radiating operation is carried out, or when the cold radiating operation is performed in combination with the general cooling operation, a large quantity of refrigerant is required. Hence, in those operation modes, it is necessary for the system to have means for temporarily receiving and discharging the refrigerant. However, the conventional air conditioning system has no means for controlling the quantity of refrigerant in the above-described manner. Thus, in a view point of controlling the quantity of refrigerant, it is rather difficult to put the conventional system in practical use.
The conventional heat storage type air conditioning system is designed as described above. Hence, the system is disadvantageous in the following points: In operation of the general cooling circuit and the cold radiating circuit in a parallel mode, the refrigerants excessively cooled and reduced in pressure in those circuits meet each other at the evaporator. Hence, the circuits are varied (become unbalanced) in the quantity of refrigerant and in the quantity of ice machine oil depending on variations in the environmental conditions or variations in the load on the side of the heat storing heat exchanger, which may make it difficult to continue the operations of the circuits.
Since the operating modes are different from one another in the required quantity of refrigerant, the quantity of refrigerant is changed for every operating mode; however, the system has no means for controlling the variations in the quantity of refrigerant. Hence, the operation of the system is not smooth, particularly in the cold storing operation. Thus, it is rather difficult to put the system in practical use.
In the case where, in the cooling operation, both the general cooling circuit and the cold radiating circuit are operated at the same time, the former circuit is operated with priority. Therefore, the degree of dependence on the cooling operation using the stored cold is not more than 50% of the total cooling load.
The conventional heat storage type air conditioning system is designed as described above. Hence, when the cold storing operation is carried out according to an "ice on coil" system, the cold storing heat exchanger may be broken by growth of the residual ice. This difficulty may be eliminated by melting the residual ice before the cold storing operation. However, melting the residual ice in this way is against the economization of energy, being disadvantageous in that electric power is used for melting it at night, and the cold (low temperature) of the residual ice cannot be utilized for the cooling operation during daytime.